Liquid sight indicators are used as liquid level gauges for vessel inventory estimation and sight flow monitors for piping system flow indication (bull's eye), or as observation sites for process equipment such as reactors, heaters, storage vessels and the like. Sight gauges are typically externally mounted on a vessel or pipe and connected between two mounting blocks attached within the range of liquid movement to indicate the presence and/or level of liquid therein. Gauges for visual indication employ transparent tubular conduits of an inert substance such as glass mounted between the mounting blocks. Breakage of the glass tube is a concern.
Many inventors have described sight gauges that improve safety by externally shielding the glass sight tube. Examples of prior art sight gauges are described in the following patents:
Kelada, U.S. Pat. No. 6,234,018 describes a safety liquid level sight gauge with a transparent sight tube coaxially disposed between mounting blocks and concentrically within a transparent shield tube which is protected by a metal sleeve with a sliding inspection window for observing the liquid level therein. The gauge includes a safety liquid level sight gauge with a transparent sight tube coaxially disposed between mounting blocks and concentrically within a transparent shield tube which is protected by a metal sleeve with a sliding inspection window for observing the liquid level therein. The gauge includes a sight tube breakage shut off system, and a leak shut off system. The breakage shut off system includes the transparent sight tube coaxially aligned between a pair of check valves within each mounting block. A check valve push rod is concentrically disposed and supported within the bore of the sight tube and urges both check valves to an open position allowing liquid to enter the bore of the sight tube. When the push rod collapses, such as when the sight tube is either cracked or broken, the check valve move to a closed position. The leak shut off system allows the check valves to move to a closed position when a pressure change occurs in the interstices formed between the transparent sight tube and the shield tube, the interstice is in communication with a diaphragm positioned on one end of a check valve activation plunger. The plunger is positioned between one end of the push rod and one check valve and moves perpendicularly to the push rod with a normal position that allows the push rod movement to be transferred to the check valve and a leak shut off position that allows the check valves to move to a closed position. A pressure change within the interstices influences the diaphragm to move the plunger to the leak shut off position closing the check valves.
Wolf, U.S. Pat. No. 5,648,607 describes a replaceable sight gauge assembly which includes two bolt assemblies. Each bolt assembly includes an entry bolt and an exit bolt, the entry bolt houses a valve which is opened when the exit bolt is mated therein the valve bolts provide a means for replacing the sight gauge.
Sheridan, U.S. Pat. No. 5,628,231 describes a sight glass for steam boilers which includes and flanges provided with molded inserts which serve to provide sealing means engaging the end surface of a sight glass. A concentrically disposed guard tube is also maintained in sealed relation to the end flanges. Tie rods to prevent excess tightening of the ended flanges are also provided.
Shank, U.S. Pat. No. 5,442,159 describes a sight gauge positioned between two spaced apart compression fittings which receive an elongated tubular transparent tube shield and a slightly longer concentrically placed sight tube.
Newman, U.S. Pat. No. 5,323,654 describes a shielded sight glass positioned between two spaced apart confronting fittings which are shielded by a polygon impact resistant plastic enclosure.
Gruett, U.S. Pat. No. 5,323,653 concerns a method for mechanically supporting a shield for a liquid gauge. The apparatus includes a support member, first and second end blocks which are slidable engagable with the support member while each has a passage way, seal borne by each of the end blocks and disposed in each of the passage ways and a transparent tube telescopingly received in the respective passage ways and defining a fluid passage way or chamber.
Bertani, U.S. Pat. No. 5,383,360 describes a column type level indicator with a means for its outward mounting through fixing screws with axial and transverse holes there through which act as ducts into the sight tube.
Ford et al., U.S. Pat. No. 5,052,224 describes a shielded vertically mounted sight gauge with a transparent pipe extending between housings, while each housing includes a flange for receiving a larger transparent shielding pipe, one flange telescopingly receives the shield with a biasing means that urges against the shield pipe so that the flange can be moved away from the shield pipe and access gained to the sight tube.
Sheridan, et al. U.S. Pat. No. 4,838,095 describes a sight glass with sampling system and includes an inner transparent glass tube an outer concentric shield tube forming an interstices between the tubes and a drain for remaining leakage caused by fracture of the inner tube.
Mills, U.S. Pat. No. 4,693,117 describes a shielded tubular gauge for placement between two spaced apart fittings connected to a vessel to show the level of liquid in the vessel, including an elongated sheet of protective material slidable received in the U-shaped edges of the frame.
Jackson, U.S. Pat. No. 4,345,468 describes a level sight monitor which includes a double tube sight element. The internal glass element is connected to the liquid system being monitored. The external tube is transparent plastic and provides a protective shield to the internal pipe and is spaced apart from the internal tube with “O” rings fitted, preferably flanged inserts. The annulus between the two tubes can be environmentally purged.
Gruett, U.S. Pat. No. 3,886,796 describes a gauge for indicating liquid level in a tank with a transparent plastic tube disposed between a pair of hollow end members. a sight tube breakage shut off system, and a leak shut off system. The breakage shut off system includes the transparent sight tube coaxially aligned between a pair of check valves within each mounting block. A check valve push rod is concentrically disposed and supported within the bore of the sight tube and urges both check valves to an open position allowing liquid to enter the bore of the sight tube. When the push rod collapses, such as when the sight tube is either cracked or broken, the check valve move to a closed position. The leak shut off system allows the check valves to move to a closed position when a pressure change occurs in the interstices formed between the transparent sight tube and the shield tube, the interstice is in communication with a diaphragm positioned on one end of a check valve activation plunger. The plunger is positioned between one end of the push rod and one check valve and moves perpendicularly to the push rod with a normal position that allows the push rod movement to be transferred to the check valve and a leak shut off position that allows the check valves to move to a closed position. A pressure change within the interstices influences the diaphragm to move the plunger to the leak shut off position closing the check valves.
In today's industries, it is sometimes necessary to store large quantities of fluids in a large container. Since fluid is added and withdrawn, it is necessary to keep an accurate measurement of the amount of fluid within the container. In order to accomplish this task, a sight glass is often used. The level of the fluid is measured by an upper and lower inlet/outlet passageway which may be connected to a cylinder which may have a glass wall which may be calibrated to indicate the level of the fluid within the container. However, the glass is susceptible to breakage and leakage especially in an industrial situation. This could lead to a serious leakage of the fluid if left unchecked. However, a ball check valve has been employed in the upper and lower passageway which will seat in the passageway when the fluid begins to excessively flow in towards the sight glass. The ball check valve obstructs the flow of the fluid and prevents the leakage of the fluid.
Commonly, the ball check valve is used in conjunction with a gage cock valve which allows the user to restrict the flow of fluid to the sight glass. The method that is used to unseat the ball check for equalizing pressure between the vessel and the gage glass is unreliable. The operator is required to turn the valve wheel of the gage cock valve many rounds to seat the valve stem which pushes the ball off the seat slightly. Once the ball is off the seat, the operator can then slightly open the valve to create a slight gap for liquid to bypass the ball check. If the valve is open to far, the ball check will seat as a result of the flow of fluid.
Consequently, there is only a small margin for error. Problems can arise if one of the ports is slightly obstructed which frequently occurs because the ports are generally small. The gage cock valve frequently freezes up due to the exposed valve stem and internal plugging. Also, the gage cock valve is prone to leaks due to several sealing surfaces which results in costly repairs.
Many valves are subject malfunction when a contaminant becomes lodged between the interior surface of the valve and a ball check. This may result in the valve becoming inoperative due to the fact that the ball check may not seat properly, allowing fluid to flow past the ball check. In order to correct this operation, the valve may be replaced which is expensive in terms of time lost and the cost of the replacement valve.